In the design of particle accelerators, especially electrostatic linear accelerators, the particular configuration and construction of the electrodes and supporting insulators is of critical importance. In conventional single and tandem Van de Graaff accelerators, the electrodes may be of planar configuration, or they may have the well-known top hat construction. The electrodes in these prior art accelerators are formed of a conductive metal, such as aluminum, stainless steel, titanium, or various alloys of these metals. The support insulators for the electrodes are typically formed of glass or of ceramic material and are bonded to the adjacent pair of electrodes to form a vacuum seal therebetween.
However, inasmuch as ceramic insulators are opaque, one cannot easily visually inspect these ceramic insulators for damage. In other particle accelerators, the electrodes are bonded to glass support insulators by soft materials, such as organic bonding agents, which may volatilize during operation of the accelerator. This volatilized organic material may be deposited on the tube electrodes, thereby requiring a time-consuming cleaning or conditioning operation.
Another problem associated with conventional prior art electrostatic linear accelerators is spallation of an insulator surface during flashover produced when it is impacted by high velocity particles. Further, insulators formed of ceramic sometimes have pipes or internal cracks therein which do not extend through or communicate with the vacuum side of the tube. However, if sufficient spalling occurs, the pipe may intercommunicate the pressure side of an accelerator tube with the vacuum side, which could result in the catastrophic loss of the expensive gas used in the pressure chamber and severe damage to the vacuum system.
In the configuration of the top hat electrodes, particle traps are defined between adjacent electrodes and are intended to prevent high velocity particles from striking the vacuum side surface of the support insulators. Although the top hat electrodes function reasonably well in preventing high velocity particles from impacting the surfaces of the insulators, the vacuum side surfaces of the insulators are not located in an "out of sight" location with respect to substantially all orbits of high velocity scattered particles. Therefore, spalling can occur in tube electrodes having the top hat electrode configuration, as well as planar electrodes.